Nephron 24 : 198 -204 (1979)
Tubular Function in Adult Polycystic Kidney Disease Harry Preuss, Kenneth Geoly, Michael Johnson, Alexander Chester. Alan Kllger and George Schreiner Departments o f Medicine and Pathology. Georgetown University Medical School, Washington. D.C.
Key Words. Adult polycystic kidney disease • PAH transport • Ammonium excretion • Renal concentration Abstract. Various tubular functions were assessed in 10 patients with polycystic kidney disease (PKD). Three rela tively unique abnormalities were apparent in many of these patients - an inability to maximally concentrate urine, a decrease in ability to lower urine pH after acute acid challenge, and an inability to excrete adequate amounts of ammonium during persistent acid challenge. The defects in urinary acidification and ammonium excretion in PKD have not been previously described.
Adult polycystic kidney disease (PKD) is a common genetic disorder, characterized structurally by numerous intrarenal cysts which enlarge with time, eventually en croaching upon normal renal tissue. These defects in mor phology, along with the natural history and clinical pre sentation of PKD. have been documented. However, tu bular function by the polycystic nephrons has not been examined extensively [1], although there is evidence that tubular dysfunction may be common in PKD. Despite the reports ofhyperchloremicacidosis[2]and uric acid nephro lithiasis [2], we know little about urinary acidification and uric acid excretion in this disorder. Relevant studies on renal handling of glucose and amino acids are unavailable although high concentrations of glucose [3] and amino acids [4] in cysts have been reported. We know that inulin and p-aminohippurate (PAH) are concentrated in many of the cysts indicating that some cysts are, in fact, working elements of the nephron [3], Be cause many cysts are in continuity with functioning parts of nephrons, it would seem likely that specific tubular dys functions may exist. Despite this, only an inability of poly cystic kidneys to concentrate urine has been well esta blished thus far [5-8]. This particular defect in tubular
function is assumed to be caused by cysts - perhaps by their encroachment upon normal renal tissue or by cystic nephrons contributing to the final urine. To determine if other specific abnormalities exist, we assessed several tubular functions in patients with PKD and compared our results to the respective glomerular filtration rates (GFR). In oursurvey, we found three tubular abnormalities among a significant number of our polycystic patients: i.e. (1) inability to concentrate urine maximally: (2) inappropriate lowering of urine pH in response to acute acid challenge, and (3) decreased renal ammonium excretion during long acid loading.
¡Methods 8 patients with PKD (strong family history and radiologic evi dence) were admitted to the Clinical Study Unit at Georgetown Uni versity Hospital for detailed studies o f tubular function. After a complete physical examination, each was maintained on a constant daily intake of fluid, sodium (Na + ), potassium (K + ), and protein appropriate for them over the 3-4 weeks necessary to complete all studies. None o f the patients were on medications nor required any during the investigation. 24-hour urines were collected daily under oil and stored at 2 C. Frequent determinations o f blood urea nitrogen
Downloaded by: Univ. of California Santa Barbara 128.111.121.42 - 3/6/2018 11:34:30 AM
Introduction
Tubular Function in PKD
199
Table I. Profile of patients with PKD Patient
Age
Sex
Flank pain
Hemat uria
CW DL
50 62
F F
+ +
+ —
ES RO RH EK RL DZ
45 35 39 40 34 32
F M F F M F
+ -
+ + + + +
Years Dx1 Family history
4 2 h
2 11 9 0 0
+ grandfather ‘bright's disease" + + + + father died - uremia
Palpable kidney
Hx o f posi BP tive urine culture
L L +R
+ +
150/80 156/80
L+ R L +R L +R L+ R L+ R R
+ + +
125/80 160/110 140/90 115/70 150/100 140/100
1 Approximate number o f years following diagnosis. L=Lcft kidney: R = right kidney.
termined on each 24-hour urine collection during this time and for 3 days thereafter. Urines were collected under toluene and refrigerated during the collection period. Ammonium was estimated by the method o f Preuss et al. [15], Urine pH was measured with a Copen hagen Radiometer pH meter. To specifically follow acid excretion following an acute NH4CI challenge [16], a separate study on another group o f patients was undertaken. 4 patients with PKD and a creatinine clearance greater than 73 ml min (mean 99 ml, min) along with 12 family members without clinical or roentgenographic evidence o f PKD (mean clear ance 109 ml/min) were evaluated as outpatients. Signed informed consent was obtained after care had been taken to explain fully to the volunteers all details o f the procedures and any potential risks. Research was carried out according to the principles outlined in the Declaration o f Helsinki and was approved by the Committee on Human Experimentation at Georgetown University Hospital. No adverse effects occurred during this study.
Results The subjects' historical data and some other findings of interest for the original group of PKD subjects are sum marized in table I. All subjects had a family history strongly suggestive of PKD. and there were radiologic findings to corroborate this diagnosis. In addition, subjects had one or more major clinical manifestations of the disease other than uremic symptoms, i.e.. hematuria, stone formation, infections, hypertension, loin pain, and/or flank fullness. Routine laboratory data obtained on entrance into the study are summarized in table II. BUN ranged from a low of 10 mg/100 ml to a high of 110 mg/10 0 ml: uric acid from
Downloaded by: Univ. of California Santa Barbara 128.111.121.42 - 3/6/2018 11:34:30 AM
(BUN), serum creatinine (Cr), phosphorus, uric acid, Na + , K + , Chloride (C I -), and CO2 content were made. Some o f the 24-hour urines were measured for urea, creatinine, uric acid, and phosphorus. These determinations were performed by the clinical laboratory at Georgetown University Hospital using standard procedures. Urine proteins [9] and amino nitrogens [10] were measured on some o f the 24-hour urine collections. Inulin clearance (Cin), PAH clearance (C paii), transport maxi mum o f PAH (TinPAH and glucose T.mGI) were measured in each subject by standard techniques [I I]. The experiments with PAH and glucose were performed at least 7 days apart. Inulin was estimated by the method o f Schreiner and Roe [12], PAH by the method of Bratton and Marshall [13], and glucose in arterial blood and urine by glucose oxidase [14], All timed urines for these particular tests were collected from indwelling bladder catheters. Maximal urinary concentrating ability was estimated by the following procedure: after 13 h overnight dehydration, sera and urines were obtained for analysis of osmolalities. Then 300 mU of aqueous pitressin were given intravenously, followed by 500 mU aqueous pitression subcutaneously at half hour intervals for l'/i h (5 doses). Sera and urines were obtained at prescribed intervals during this time, and the osmolalities were measured with an Advanced Osmometer. In our hands, normal controls eventually exceeded a urine to plasma ratio (U/P) o f 3.5. Some aspects of renal acidification (pH and ammonium excretion) were assessed over a matter o f days. 2 additional PKD patients (KO, 24-ycar-old white female with a CAii) were within normal limits in patients with Cm of greater than 20 ml/min, increases in filtration frac tions were noted when Cm was below 20 ml/min (CW, DL, and ES). In the 4 azotemic patients (CW, DL. Es. and RL: BUN 30 mg% or greater), TmGI was depressed to the same degree as the GFR. This is evidenced by a near similar ratio TmGl/Cm. However. TmPAH was particularly low, de pressed disproportionately to the GFR in the azotemic PKD subjects (CW, DL. ES. RL). None of the subjects, including those with the higher inulin clearances, were able to maximally concentrate their urine, even after exogenous pitressin administration. Of
Downloaded by: Univ. of California Santa Barbara 128.111.121.42 - 3/6/2018 11:34:30 AM
U/P
201
Tubular Function in PKD
Discussion Tubular function in PKD has not been systematically examined [I ], Indeed, from various different studies tubular dysfunction is suggested. Hyperchloremic acidosis [2], hyperuricemia [18] and uric acid lithiasis [2] may all indicate tubular abnormalities. Although our review of many functions reveals findings not unlike those seen in end stage kidneys resulting from other renal disorders, we noted three findings which were unusual. All showed a defect in maximal urine concen-
Oays
Fig. 1. Ammonium excretion above baseline in 6 control and 10 PCKD subjects during ammonium chloride challenge (days 1 4 ). Recovery period is depicted also (day 5-7). The gray envelope re presents the controls and the striped envelope represents the PKD subjects. Dark areas portray overlap in results.
trating ability regardless of the GFR. 2 of 4 did not decrease their urine pH appropriately in response to acute acid challenge. Finally, we found an inability in our PKD sub jects to generate a normal rise in urinary ammonium ex cretion after long acid loading. We even noted this, in 4 of 7 subjects when ammonium excretion was factored by GFR. An inability of PKD patients to maximally concentrate their urine has been described previously [5-8]. Because it is present in some PKD patients before significant im pairment of GFR is seen, it probably represents an early specific tubular defect. The pathophysiology behind this has been investigated in detail and the defect localized to the collecting duct [7], Our new finding is that many PKD subjects were unable to lower urine pH normally following acute acid challenge and could not raise their ammonium excretion appropri ately in response to prolonged acid challenge. 2 o f4 subjects could not lower urine pH below 5.3 suggesting a defect in distal tubular production and/or the ability to maintain an adequate hydrogen ion gradient. This defect would be due to the same defect in the collecting duct which causes the concentrating defect [7], 10 PK D patients were followed during persistent NH iCI ingestion. Relative to 6 normal control subjects, this group
Downloaded by: Univ. of California Santa Barbara 128.111.121.42 - 3/6/2018 11:34:30 AM
particular note are patients DZ and EK with Cm of 93 and 72 ml/min, respectively; neither was able to generate a maximum U/P osmolality ratio greater than 2.4. well below our normal minimum, 3.5. Persistent acid challenge with ammonium chloride re vealed an abnormal pattern of acid excretion in PKD pa tients. Ammonium excretion above baseline appeared to be lower than control (fig. I). Only a small portion of the envelope depicting ammonium excretion in PKD over lapped that of the 6 controls. To determine if this was totally secondary to the degree of renal mass loss, ammonium ex cretion was factored by GFR. It seemed unreasonable to handle the data from the 3 subjects with Cm less than 10 ml/ min like this; and so, only data from the 7 PKD patients with GFR (Cm) above 48 ml/min were analyzed (fig.2). When compared in this manner. 3 of the patients' (KO. PO, ER) values fell within normal ranges, albeit in the lower half of this range. 4 of the polycystic subjects (RO. DZ. RH, RL) excreted less ammonium than could be accounted for by mass loss alone. The daily excretions of Cl . Na , plus K , and NFI.i . above baseline are depicted in a manner popularized by Gamble [\1] for a control and a representative PKD (RH) with decreased ammonium ex cretion (fig. 3.4). Whereas, the kidneys of the normal pa tient replace the early loss of Na and K with ammonium during the persistent acid challenge, the PKD patient (Cm 68.7) continued to lose electrolytes throughout the chal lenge. never raising ammonium excretion to a level appro priate for the anion load. In a separate group of 16 different subjects (4 patients with PKD and 12 kindred who had no evidence of disease), acute acid challenges were given. According to the criteria of Wrong and Davies [16], 11 of the normal kindred showed a normal response, i.e., a urine pH 5.3 or below. I subject reached 5.4 as his lowest pH. Only 4 of the new PKD pa tients were acutely challenged; however, 2 had urine pH greater than 5.3 (5.6 and 6.6).
202
Preuss/Geoiy/Johnson Chester Kliger/Schreiner
100
60
0
Days
1
0 Days
1
2
3
4
Fig. 2. Ammonium excretion above baseline during ammoni um excretion in 7 PKD subjects. The envelope in each portion of the figure depicts the results from the 6 controls. Results arc fac tored in order to represent am monium excretion per 100 ml o f GFR.
Days
Fig. 3. Excretion o f ions by a control subject following an am monium chloride challenge given orally. Recovery period is also depicted. Rates o f excretion are plotted as increments over results from a baseline period. • = Chloride; a = Na + K; ■ = N H .i+ .
Fig. 4. Excretion o f ions by a PKD subject following an am monium chloride challenge given orally. Recovery period is also depicted. Rates o f excretion are plotted as increments over results from a baseline period. • = Chloride: A = Na + K; ■ = NH.i + .
displayed poor ammonium excretion. Why did this occur? Ammonium excretion is affect by urine pH [19] urine volume [19], and by renal production [20]. The former two are not important here for the following reasons. At urine pH below 6.5 in humans, volume plays only a minor role in regulating ammonium excretion; and during acid chal lenge, our patients did decrease urine pH below 6.5. Finally, since ammonia enters the tubular lumen as a gas [20], it is unlikely that any but the most gross changes in medullary architecture would affect its excretion. Therefore, we con
clude that the major decrease in excretion is secondary to decreased production. Despite the probability that am monia is produced in proximal tubules [21,22] we found no general evidence of otherproximal tubular dysfunctions. Other tubular functions appeared intact. No glucosuria, uricosuria, nor amino aciduria were noted. The exagger ated phosphaturia observed in the patients with the lowest filtration rate probably relates to a secondary hypaerprathyroidism rather than a specific tubular defect [23]. We noted a high filtration fraction (Cjn)/Cj.AH) and a dispro
Downloaded by: Univ. of California Santa Barbara 128.111.121.42 - 3/6/2018 11:34:30 AM
Days
portionately low TmPAH compared to Cin in 4 azotemic subjects. In these 4. the decrease in PAH transport was out of proportion to the drop in GFR, contrasted to TmGl which decreased proportionately with the Cm. Since we noted this disorder only in those patients with azotemia, and it has been reported previously in patients with azo temia from other renal diseases [24], it seems unlikely that this represents a specific tubular defect of PKD patients. Inadequate ammonium excretion in end-stage renal disease has been attributed to decreased renal mass [2527]. Factoring values by GFR usually suggests that normal or even supernormal production exists in the remaining functioning nephrons of end-stage renal disease [26], When we factored ammonium excretion by the respective GFR, 4 of the PKD patients compared to control showed de creased ammonium excretion. Therefore, it seems likely that this does represent a tubular malfunction in. at least, many PKD patients. Poor renal ammonia production has been reported in cystic renal disease. A defect in ammonium excretion has been reported in a single case of medullary cystic disease [28], As a first approximation, we surveyed tubular function in patients with PKD and found three unique tubular dys functions - inability to concentrate urine, to acidify the urine properly following acute acid challenge, and to ex crete ammonium adequately. The first malfunction has been reported previously [5-8]. The latter two have not. Obviously, more work will have to be performed on each defect in order to determine its extent and pathogenesis. For the moment, we can only speculate that the inability to lower urine pH in acute acidosis, like the concentrating defect [7], may be due to a common malfunction in the collecting duct. However, such a defect would not explain the poor excretion of ammonium [20-21].
Acknowledgements This work was supported by a grant from the National Capital Area Branch of the National Kidney Foundation and by a grant (MO-l-RR-60) from the General Research Centers Program o f the Division of Research Resources, National Institutes o f Health.
References 1 Papper, S.: Cystic disorders; in Clinical nephrology, pp.436-448 (Boston, Little Brown, Boston 1971). 2 Hamburger, J.: Richet, G.; Crosnier, J.; Funck-Bretano, J.L.; Antoine. B.; Duerot, H.; Mary, J.P.. and DeMontera, H.: Nephrology II, pp. 1070 (Philadelphia, Saunders 1968).
203
3 Lambert, P. P.: Polycystic disease o f the kidney. Archs Path. 44: 34-58 (1947). 4 Gardner, K .D .: Composition o f fluid in twelve cysts o f a poly cystic kidney. New Engl. J. Med. 281: 985-988 (1969). 5 Prat, V.: NSktere Udaje Ke Klinickemu Obrazu Polycystickych Ledvin Dospilych. Cas. Led. Cesk. 99: 1332-1339 (I960). 6 Prat, V.: Vysetreni Oddelenc Ledvinne Funkce U Nemocnych Polycystickymi Ledvinami. Cas. Lek. desk. 100: 161-165 (1961). 7 Martinez-Maldonado, M.: Yium, J.J.: Ednoyan, G., and Suki, W .N.: Adult polycystic kidney disease: studies o f the defect in urine concentration. Kidney int. 2: 107-113 (1972). 8 D'Angelo, A.; Mioni, G.; Ossi, E.; Lupo, A.; Volvo, E., and Maschio, G.: Alterations in renal tubular sodium and water transport in polycystic kidney disease. Clin. Nephrol. 3: 99-105 (1975). 9 Shevsky, M.C. and Stafford. D. D.: A clinical method for the estimation o f protein in urine and other body fluids. Archs intern. Med. 32: 222-225 (1923). 10 Rosen, H .: A modified ninhydrin colorimetric analysis for amino acids. Archs Biochcm. biophys. 67: 10-15 (1957). 11 Smith, H.W.: Measurement of renal clearances; in Principles of renal physiology, pp. 196-214 (Oxford University Press, New York 1957). 12 Schreiner, G.E. and Roe: Determination o f inulin by means of resorcinol. Proc. Soc. exp. Biol. Med. 74: 117-120 (1950). 13 Bratton, A.C. and Marshall, E.K., Jr.: A new coupling compo nent for sulfanilamide determination. J. biol. Chem. 128: 537-550 (1939). 14 Bergmeycr, H.U . and Bernt, E.: D-Glucose: determination with glucose oxidase and peroxidase; in Mcthodsofenzymaticanalysis, pp. 123-130 (Academic Press, New York 1965). 15 Preuss, H.G.; Bise, B.W..and Schreiner, G .E .: The determination o f glutamine in plasma and urine. Clin. Chem. 12:329-337 (1966). 16 Wrong, O. and Davies, H.E. F .: The excretion of acid in renal disease. Q. Jl. Med. 28: 259-313 (1959). 17 Gamble. J.L.: Chart 38; in Chemical anatomy; physiology and pathology, p.89 (Harvard University Press, Cambridge 1954). 18 Newcombe, D .S.: Gouty arthritis and polycystic kidney disease. Ann. intern. Med. 79: 605 (1973). 19 Richterich, R.: Physio-chemical factors determining ammonia excretion. Helv. physiol, pharmacol. Acta 20: 326-345 (1962). 20 Denis, G.; Preuss, H., and Pitts, R.: The PNH3 o f renal tubular cells. J. clin. Invest. 43: 571 582 (1964). 21 Glabman, S.; Klose, R.M ., and Giebisch, G.: Micropuncture study o f ammonia excretion in the rat. Am. J. Physiol. 205: 127 132(1963). 22 Pitts, R.F.: Handbook o f physiology, pp.445-496 (American Physiological Society, Washington 1973). 23 Reiss, E.: Canterbury, J.M ., and Kantcr, A.: Circulating para thyroid hormone concentration in chronic renal insufficiency. Archs intern. Med. 124: 417-422 (1969). 24 Smith, H.W.: Diseases o f the kidney and urinary tract; The Kidney, 836-887 (Oxford Univ. Press, New York 1951). 25 Elkinton, J.R.: Hydrogen ion turnover in health and in renal disease. Ann. intern. Med. 57: 660-684 (1962). 26 Dorhout-Mees, E.J.; Machado, M.; Slatopolsky, E.; Klahr, S., and Bricker, N .S.: The functional adaptation o f the diseased kidney. III. Ammonium excretion. J. clin. Invest. 45: 289-296 (1966).
Downloaded by: Univ. of California Santa Barbara 128.111.121.42 - 3/6/2018 11:34:30 AM
Tubular Function in PKD
27 Preuss, H.G. and Goldin, H.: Ammoniagenesis in growing nephrons o f uninephrectomized rats. Lab. Invest. 31: 454-457 (1974). 28 Levin. N. W. ; Rosenberg. B. ; Zwi, S., and Reid, F. P. : Medullary cystic disease o f the kidney, with some observations on ammonium excretion. Am. J. Med. 30: 807-812 (1961 ).
Preuss/Geoly/Johnson/Chester/Kliger/Schreiner
Accepted: February 2, 1979
Dr. Harry G. Preuss, Georgeiown University Medical School, 153 Basic Science Building, 3900 Reservoir Road, NVV, Washington, DC 20007 (USA)
Downloaded by: Univ. of California Santa Barbara 128.111.121.42 - 3/6/2018 11:34:30 AM
204
Tubular Function in Adult Polycystic Kidney Disease Harry Preuss, Kenneth Geoly, Michael Johnson, Alexander Chester. Alan Kllger and George Schreiner Departments o f Medicine and Pathology. Georgetown University Medical School, Washington. D.C.
Key Words. Adult polycystic kidney disease • PAH transport • Ammonium excretion • Renal concentration Abstract. Various tubular functions were assessed in 10 patients with polycystic kidney disease (PKD). Three rela tively unique abnormalities were apparent in many of these patients - an inability to maximally concentrate urine, a decrease in ability to lower urine pH after acute acid challenge, and an inability to excrete adequate amounts of ammonium during persistent acid challenge. The defects in urinary acidification and ammonium excretion in PKD have not been previously described.
Adult polycystic kidney disease (PKD) is a common genetic disorder, characterized structurally by numerous intrarenal cysts which enlarge with time, eventually en croaching upon normal renal tissue. These defects in mor phology, along with the natural history and clinical pre sentation of PKD. have been documented. However, tu bular function by the polycystic nephrons has not been examined extensively [1], although there is evidence that tubular dysfunction may be common in PKD. Despite the reports ofhyperchloremicacidosis[2]and uric acid nephro lithiasis [2], we know little about urinary acidification and uric acid excretion in this disorder. Relevant studies on renal handling of glucose and amino acids are unavailable although high concentrations of glucose [3] and amino acids [4] in cysts have been reported. We know that inulin and p-aminohippurate (PAH) are concentrated in many of the cysts indicating that some cysts are, in fact, working elements of the nephron [3], Be cause many cysts are in continuity with functioning parts of nephrons, it would seem likely that specific tubular dys functions may exist. Despite this, only an inability of poly cystic kidneys to concentrate urine has been well esta blished thus far [5-8]. This particular defect in tubular
function is assumed to be caused by cysts - perhaps by their encroachment upon normal renal tissue or by cystic nephrons contributing to the final urine. To determine if other specific abnormalities exist, we assessed several tubular functions in patients with PKD and compared our results to the respective glomerular filtration rates (GFR). In oursurvey, we found three tubular abnormalities among a significant number of our polycystic patients: i.e. (1) inability to concentrate urine maximally: (2) inappropriate lowering of urine pH in response to acute acid challenge, and (3) decreased renal ammonium excretion during long acid loading.
¡Methods 8 patients with PKD (strong family history and radiologic evi dence) were admitted to the Clinical Study Unit at Georgetown Uni versity Hospital for detailed studies o f tubular function. After a complete physical examination, each was maintained on a constant daily intake of fluid, sodium (Na + ), potassium (K + ), and protein appropriate for them over the 3-4 weeks necessary to complete all studies. None o f the patients were on medications nor required any during the investigation. 24-hour urines were collected daily under oil and stored at 2 C. Frequent determinations o f blood urea nitrogen
Downloaded by: Univ. of California Santa Barbara 128.111.121.42 - 3/6/2018 11:34:30 AM
Introduction
Tubular Function in PKD
199
Table I. Profile of patients with PKD Patient
Age
Sex
Flank pain
Hemat uria
CW DL
50 62
F F
+ +
+ —
ES RO RH EK RL DZ
45 35 39 40 34 32
F M F F M F
+ -
+ + + + +
Years Dx1 Family history
4 2 h
2 11 9 0 0
+ grandfather ‘bright's disease" + + + + father died - uremia
Palpable kidney
Hx o f posi BP tive urine culture
L L +R
+ +
150/80 156/80
L+ R L +R L +R L+ R L+ R R
+ + +
125/80 160/110 140/90 115/70 150/100 140/100
1 Approximate number o f years following diagnosis. L=Lcft kidney: R = right kidney.
termined on each 24-hour urine collection during this time and for 3 days thereafter. Urines were collected under toluene and refrigerated during the collection period. Ammonium was estimated by the method o f Preuss et al. [15], Urine pH was measured with a Copen hagen Radiometer pH meter. To specifically follow acid excretion following an acute NH4CI challenge [16], a separate study on another group o f patients was undertaken. 4 patients with PKD and a creatinine clearance greater than 73 ml min (mean 99 ml, min) along with 12 family members without clinical or roentgenographic evidence o f PKD (mean clear ance 109 ml/min) were evaluated as outpatients. Signed informed consent was obtained after care had been taken to explain fully to the volunteers all details o f the procedures and any potential risks. Research was carried out according to the principles outlined in the Declaration o f Helsinki and was approved by the Committee on Human Experimentation at Georgetown University Hospital. No adverse effects occurred during this study.
Results The subjects' historical data and some other findings of interest for the original group of PKD subjects are sum marized in table I. All subjects had a family history strongly suggestive of PKD. and there were radiologic findings to corroborate this diagnosis. In addition, subjects had one or more major clinical manifestations of the disease other than uremic symptoms, i.e.. hematuria, stone formation, infections, hypertension, loin pain, and/or flank fullness. Routine laboratory data obtained on entrance into the study are summarized in table II. BUN ranged from a low of 10 mg/100 ml to a high of 110 mg/10 0 ml: uric acid from
Downloaded by: Univ. of California Santa Barbara 128.111.121.42 - 3/6/2018 11:34:30 AM
(BUN), serum creatinine (Cr), phosphorus, uric acid, Na + , K + , Chloride (C I -), and CO2 content were made. Some o f the 24-hour urines were measured for urea, creatinine, uric acid, and phosphorus. These determinations were performed by the clinical laboratory at Georgetown University Hospital using standard procedures. Urine proteins [9] and amino nitrogens [10] were measured on some o f the 24-hour urine collections. Inulin clearance (Cin), PAH clearance (C paii), transport maxi mum o f PAH (TinPAH and glucose T.mGI) were measured in each subject by standard techniques [I I]. The experiments with PAH and glucose were performed at least 7 days apart. Inulin was estimated by the method o f Schreiner and Roe [12], PAH by the method of Bratton and Marshall [13], and glucose in arterial blood and urine by glucose oxidase [14], All timed urines for these particular tests were collected from indwelling bladder catheters. Maximal urinary concentrating ability was estimated by the following procedure: after 13 h overnight dehydration, sera and urines were obtained for analysis of osmolalities. Then 300 mU of aqueous pitressin were given intravenously, followed by 500 mU aqueous pitression subcutaneously at half hour intervals for l'/i h (5 doses). Sera and urines were obtained at prescribed intervals during this time, and the osmolalities were measured with an Advanced Osmometer. In our hands, normal controls eventually exceeded a urine to plasma ratio (U/P) o f 3.5. Some aspects of renal acidification (pH and ammonium excretion) were assessed over a matter o f days. 2 additional PKD patients (KO, 24-ycar-old white female with a CAii) were within normal limits in patients with Cm of greater than 20 ml/min, increases in filtration frac tions were noted when Cm was below 20 ml/min (CW, DL, and ES). In the 4 azotemic patients (CW, DL. Es. and RL: BUN 30 mg% or greater), TmGI was depressed to the same degree as the GFR. This is evidenced by a near similar ratio TmGl/Cm. However. TmPAH was particularly low, de pressed disproportionately to the GFR in the azotemic PKD subjects (CW, DL. ES. RL). None of the subjects, including those with the higher inulin clearances, were able to maximally concentrate their urine, even after exogenous pitressin administration. Of
Downloaded by: Univ. of California Santa Barbara 128.111.121.42 - 3/6/2018 11:34:30 AM
U/P
201
Tubular Function in PKD
Discussion Tubular function in PKD has not been systematically examined [I ], Indeed, from various different studies tubular dysfunction is suggested. Hyperchloremic acidosis [2], hyperuricemia [18] and uric acid lithiasis [2] may all indicate tubular abnormalities. Although our review of many functions reveals findings not unlike those seen in end stage kidneys resulting from other renal disorders, we noted three findings which were unusual. All showed a defect in maximal urine concen-
Oays
Fig. 1. Ammonium excretion above baseline in 6 control and 10 PCKD subjects during ammonium chloride challenge (days 1 4 ). Recovery period is depicted also (day 5-7). The gray envelope re presents the controls and the striped envelope represents the PKD subjects. Dark areas portray overlap in results.
trating ability regardless of the GFR. 2 of 4 did not decrease their urine pH appropriately in response to acute acid challenge. Finally, we found an inability in our PKD sub jects to generate a normal rise in urinary ammonium ex cretion after long acid loading. We even noted this, in 4 of 7 subjects when ammonium excretion was factored by GFR. An inability of PKD patients to maximally concentrate their urine has been described previously [5-8]. Because it is present in some PKD patients before significant im pairment of GFR is seen, it probably represents an early specific tubular defect. The pathophysiology behind this has been investigated in detail and the defect localized to the collecting duct [7], Our new finding is that many PKD subjects were unable to lower urine pH normally following acute acid challenge and could not raise their ammonium excretion appropri ately in response to prolonged acid challenge. 2 o f4 subjects could not lower urine pH below 5.3 suggesting a defect in distal tubular production and/or the ability to maintain an adequate hydrogen ion gradient. This defect would be due to the same defect in the collecting duct which causes the concentrating defect [7], 10 PK D patients were followed during persistent NH iCI ingestion. Relative to 6 normal control subjects, this group
Downloaded by: Univ. of California Santa Barbara 128.111.121.42 - 3/6/2018 11:34:30 AM
particular note are patients DZ and EK with Cm of 93 and 72 ml/min, respectively; neither was able to generate a maximum U/P osmolality ratio greater than 2.4. well below our normal minimum, 3.5. Persistent acid challenge with ammonium chloride re vealed an abnormal pattern of acid excretion in PKD pa tients. Ammonium excretion above baseline appeared to be lower than control (fig. I). Only a small portion of the envelope depicting ammonium excretion in PKD over lapped that of the 6 controls. To determine if this was totally secondary to the degree of renal mass loss, ammonium ex cretion was factored by GFR. It seemed unreasonable to handle the data from the 3 subjects with Cm less than 10 ml/ min like this; and so, only data from the 7 PKD patients with GFR (Cm) above 48 ml/min were analyzed (fig.2). When compared in this manner. 3 of the patients' (KO. PO, ER) values fell within normal ranges, albeit in the lower half of this range. 4 of the polycystic subjects (RO. DZ. RH, RL) excreted less ammonium than could be accounted for by mass loss alone. The daily excretions of Cl . Na , plus K , and NFI.i . above baseline are depicted in a manner popularized by Gamble [\1] for a control and a representative PKD (RH) with decreased ammonium ex cretion (fig. 3.4). Whereas, the kidneys of the normal pa tient replace the early loss of Na and K with ammonium during the persistent acid challenge, the PKD patient (Cm 68.7) continued to lose electrolytes throughout the chal lenge. never raising ammonium excretion to a level appro priate for the anion load. In a separate group of 16 different subjects (4 patients with PKD and 12 kindred who had no evidence of disease), acute acid challenges were given. According to the criteria of Wrong and Davies [16], 11 of the normal kindred showed a normal response, i.e., a urine pH 5.3 or below. I subject reached 5.4 as his lowest pH. Only 4 of the new PKD pa tients were acutely challenged; however, 2 had urine pH greater than 5.3 (5.6 and 6.6).
202
Preuss/Geoiy/Johnson Chester Kliger/Schreiner
100
60
0
Days
1
0 Days
1
2
3
4
Fig. 2. Ammonium excretion above baseline during ammoni um excretion in 7 PKD subjects. The envelope in each portion of the figure depicts the results from the 6 controls. Results arc fac tored in order to represent am monium excretion per 100 ml o f GFR.
Days
Fig. 3. Excretion o f ions by a control subject following an am monium chloride challenge given orally. Recovery period is also depicted. Rates o f excretion are plotted as increments over results from a baseline period. • = Chloride; a = Na + K; ■ = N H .i+ .
Fig. 4. Excretion o f ions by a PKD subject following an am monium chloride challenge given orally. Recovery period is also depicted. Rates o f excretion are plotted as increments over results from a baseline period. • = Chloride: A = Na + K; ■ = NH.i + .
displayed poor ammonium excretion. Why did this occur? Ammonium excretion is affect by urine pH [19] urine volume [19], and by renal production [20]. The former two are not important here for the following reasons. At urine pH below 6.5 in humans, volume plays only a minor role in regulating ammonium excretion; and during acid chal lenge, our patients did decrease urine pH below 6.5. Finally, since ammonia enters the tubular lumen as a gas [20], it is unlikely that any but the most gross changes in medullary architecture would affect its excretion. Therefore, we con
clude that the major decrease in excretion is secondary to decreased production. Despite the probability that am monia is produced in proximal tubules [21,22] we found no general evidence of otherproximal tubular dysfunctions. Other tubular functions appeared intact. No glucosuria, uricosuria, nor amino aciduria were noted. The exagger ated phosphaturia observed in the patients with the lowest filtration rate probably relates to a secondary hypaerprathyroidism rather than a specific tubular defect [23]. We noted a high filtration fraction (Cjn)/Cj.AH) and a dispro
Downloaded by: Univ. of California Santa Barbara 128.111.121.42 - 3/6/2018 11:34:30 AM
Days
portionately low TmPAH compared to Cin in 4 azotemic subjects. In these 4. the decrease in PAH transport was out of proportion to the drop in GFR, contrasted to TmGl which decreased proportionately with the Cm. Since we noted this disorder only in those patients with azotemia, and it has been reported previously in patients with azo temia from other renal diseases [24], it seems unlikely that this represents a specific tubular defect of PKD patients. Inadequate ammonium excretion in end-stage renal disease has been attributed to decreased renal mass [2527]. Factoring values by GFR usually suggests that normal or even supernormal production exists in the remaining functioning nephrons of end-stage renal disease [26], When we factored ammonium excretion by the respective GFR, 4 of the PKD patients compared to control showed de creased ammonium excretion. Therefore, it seems likely that this does represent a tubular malfunction in. at least, many PKD patients. Poor renal ammonia production has been reported in cystic renal disease. A defect in ammonium excretion has been reported in a single case of medullary cystic disease [28], As a first approximation, we surveyed tubular function in patients with PKD and found three unique tubular dys functions - inability to concentrate urine, to acidify the urine properly following acute acid challenge, and to ex crete ammonium adequately. The first malfunction has been reported previously [5-8]. The latter two have not. Obviously, more work will have to be performed on each defect in order to determine its extent and pathogenesis. For the moment, we can only speculate that the inability to lower urine pH in acute acidosis, like the concentrating defect [7], may be due to a common malfunction in the collecting duct. However, such a defect would not explain the poor excretion of ammonium [20-21].
Acknowledgements This work was supported by a grant from the National Capital Area Branch of the National Kidney Foundation and by a grant (MO-l-RR-60) from the General Research Centers Program o f the Division of Research Resources, National Institutes o f Health.
References 1 Papper, S.: Cystic disorders; in Clinical nephrology, pp.436-448 (Boston, Little Brown, Boston 1971). 2 Hamburger, J.: Richet, G.; Crosnier, J.; Funck-Bretano, J.L.; Antoine. B.; Duerot, H.; Mary, J.P.. and DeMontera, H.: Nephrology II, pp. 1070 (Philadelphia, Saunders 1968).
203
3 Lambert, P. P.: Polycystic disease o f the kidney. Archs Path. 44: 34-58 (1947). 4 Gardner, K .D .: Composition o f fluid in twelve cysts o f a poly cystic kidney. New Engl. J. Med. 281: 985-988 (1969). 5 Prat, V.: NSktere Udaje Ke Klinickemu Obrazu Polycystickych Ledvin Dospilych. Cas. Led. Cesk. 99: 1332-1339 (I960). 6 Prat, V.: Vysetreni Oddelenc Ledvinne Funkce U Nemocnych Polycystickymi Ledvinami. Cas. Lek. desk. 100: 161-165 (1961). 7 Martinez-Maldonado, M.: Yium, J.J.: Ednoyan, G., and Suki, W .N.: Adult polycystic kidney disease: studies o f the defect in urine concentration. Kidney int. 2: 107-113 (1972). 8 D'Angelo, A.; Mioni, G.; Ossi, E.; Lupo, A.; Volvo, E., and Maschio, G.: Alterations in renal tubular sodium and water transport in polycystic kidney disease. Clin. Nephrol. 3: 99-105 (1975). 9 Shevsky, M.C. and Stafford. D. D.: A clinical method for the estimation o f protein in urine and other body fluids. Archs intern. Med. 32: 222-225 (1923). 10 Rosen, H .: A modified ninhydrin colorimetric analysis for amino acids. Archs Biochcm. biophys. 67: 10-15 (1957). 11 Smith, H.W.: Measurement of renal clearances; in Principles of renal physiology, pp. 196-214 (Oxford University Press, New York 1957). 12 Schreiner, G.E. and Roe: Determination o f inulin by means of resorcinol. Proc. Soc. exp. Biol. Med. 74: 117-120 (1950). 13 Bratton, A.C. and Marshall, E.K., Jr.: A new coupling compo nent for sulfanilamide determination. J. biol. Chem. 128: 537-550 (1939). 14 Bergmeycr, H.U . and Bernt, E.: D-Glucose: determination with glucose oxidase and peroxidase; in Mcthodsofenzymaticanalysis, pp. 123-130 (Academic Press, New York 1965). 15 Preuss, H.G.; Bise, B.W..and Schreiner, G .E .: The determination o f glutamine in plasma and urine. Clin. Chem. 12:329-337 (1966). 16 Wrong, O. and Davies, H.E. F .: The excretion of acid in renal disease. Q. Jl. Med. 28: 259-313 (1959). 17 Gamble. J.L.: Chart 38; in Chemical anatomy; physiology and pathology, p.89 (Harvard University Press, Cambridge 1954). 18 Newcombe, D .S.: Gouty arthritis and polycystic kidney disease. Ann. intern. Med. 79: 605 (1973). 19 Richterich, R.: Physio-chemical factors determining ammonia excretion. Helv. physiol, pharmacol. Acta 20: 326-345 (1962). 20 Denis, G.; Preuss, H., and Pitts, R.: The PNH3 o f renal tubular cells. J. clin. Invest. 43: 571 582 (1964). 21 Glabman, S.; Klose, R.M ., and Giebisch, G.: Micropuncture study o f ammonia excretion in the rat. Am. J. Physiol. 205: 127 132(1963). 22 Pitts, R.F.: Handbook o f physiology, pp.445-496 (American Physiological Society, Washington 1973). 23 Reiss, E.: Canterbury, J.M ., and Kantcr, A.: Circulating para thyroid hormone concentration in chronic renal insufficiency. Archs intern. Med. 124: 417-422 (1969). 24 Smith, H.W.: Diseases o f the kidney and urinary tract; The Kidney, 836-887 (Oxford Univ. Press, New York 1951). 25 Elkinton, J.R.: Hydrogen ion turnover in health and in renal disease. Ann. intern. Med. 57: 660-684 (1962). 26 Dorhout-Mees, E.J.; Machado, M.; Slatopolsky, E.; Klahr, S., and Bricker, N .S.: The functional adaptation o f the diseased kidney. III. Ammonium excretion. J. clin. Invest. 45: 289-296 (1966).
Downloaded by: Univ. of California Santa Barbara 128.111.121.42 - 3/6/2018 11:34:30 AM
Tubular Function in PKD
27 Preuss, H.G. and Goldin, H.: Ammoniagenesis in growing nephrons o f uninephrectomized rats. Lab. Invest. 31: 454-457 (1974). 28 Levin. N. W. ; Rosenberg. B. ; Zwi, S., and Reid, F. P. : Medullary cystic disease o f the kidney, with some observations on ammonium excretion. Am. J. Med. 30: 807-812 (1961 ).
Preuss/Geoly/Johnson/Chester/Kliger/Schreiner
Accepted: February 2, 1979
Dr. Harry G. Preuss, Georgeiown University Medical School, 153 Basic Science Building, 3900 Reservoir Road, NVV, Washington, DC 20007 (USA)
Downloaded by: Univ. of California Santa Barbara 128.111.121.42 - 3/6/2018 11:34:30 AM
204
